THE GEOLOGIC AND GEOMORPHIC HISTORY OF

THE APPALACHIAN FALL LINE IN SOUTH CAROLINA

By Alicia Fischer

What is a Fall Line?

• Geomorphologic unconformity

• A high, crystalline area and a sedimentary coast

• Waterfalls and/or rapids

• Lack of knowledge

The Fall Line and SC

• The state most influenced by the fall line is South Carolina

• Divides SC in half (Columbia)

• Key role in the formation of the state

Characteristics of the Fall Line

• Spans 135 miles across SC

• The boundary between the Piedmont and the Coastal Plain

• Geologically – is made of bedrock

• Geomorphically – the last appearance of bedrock downstream

• Decrease in elevation from erosion (Piedmont vs Coastal Plain)

• Reliefs up to 300 feet in a short distance

Characteristics of the Fall Line (cont.)

• Quick deep drops disrupt river flow

• Rivers downcut to reach the low Coastal Plain

• High river gradients

• Rough character with rapids, gorges, and waterfalls

• Fluvial erosion (Piedmont) and deposition (Coastal Plain)

Geologic/Geomorphic History of SC: Pre-Cambrian

• Lava World

• 1.2 billion years ago, the first rocks created in what will become South Carolina

• The Grenville Orogeny created the eastern U.S. (SC’s Blue Ridge)

Geologic/Geomorphic History of SC: Paleozoic

• Appalachian Orogeny: most important in SC’s formation

• Alleghanian orogeny formed the Appalachian Mountain

• Rapid uplift and deformation in Blue Ridge (crystalline)

• Half of present-day SC formed during the Alleghanian

Orogeny (Piedmont)

Geologic/Geomorphic History of SC: Mesozoic

• Reinvigorated Grenville and Appalachian materials

• Fault-prone rift basins (erosion)

• Reversed rivers to east (drainage divide)

• Waves of erosion deteriorated Appalachian peaks

• Rivers deposit sediment to Mesozoic shoreline (Coastal Plain)

Geologic/Geomorphic History of SC: Cenozoic

• Sediment continually deposited by gravity and fluvial processes

• Epeirogeny across the Blue Ridge and Piedmont (erosion)

• Spans the Coastal Plain past Mesozoic shoreline (120 miles)

 

Geologic/Geomorphic History of the Fall Line

• Resistant crystalline Blue Ridge (31 meters per million years)

• Piedmont metasedimentary peneplain (16 meters per million years)

• Flat sedimentary Coastal Plain (depositional area)

• Fall line lies between Piedmont and Coastal Plain

• Made of bedrock and was the old Mesozoic shoreline

Fall Line Formational Hypothesis #1:Faulting

• Numerous faults lie in the fall line

• Small localized faults exist throughout SC

• Crosscut South Carolinian geological terrain

• Faulting exists only in a few sections of the fall line

• False Hypothesis

Fall Line Formational Hypothesis #2:Coastal Emergence/Erosion

• Coastal Plain once extended over Piedmont

• Rivers did not erode the Coastal Plain

• Regional disruptions created its hilly topography

• Through-flowing rivers caused Coastal Plain’s erosion

• Restricted to the coast and east of the Piedmont

Fall Line Formational Hypothesis #2:Coastal Emergence/Erosion (cont.)

• Research shows this coverage was too overstated

• Drainage patterns in some locations support this hypothesis

• Upland – dendritic

• Coastal Plain materials 40 km above the fall line

Fall Line Formational Hypothesis #3:Peneplain intersection and unconformity

• Two ancient peneplains crosscut

• The fall line is Piedmont’s stripped face

• Only Piedmont existed (uplifted and tilted into Atlantic)

• Deposition and extension of Coastal Plain on Piedmont

• Rivers flowed from the Piedmont to the Coastal Plain

• The erosional contact exposed bedrock

Fall Line Formational Hypothesis #3:Peneplain intersection & unconformity (cont.)

• Deep drilling into the Coastal Plain exposed the underlying Piedmont

• Coastal Plain depth extends from 0 feet to over 4,000 feet

• Hypotheses 2 and 3 explain fall line’s origin

Figure 11-4, South Carolina “Fall Line ”

Relocation and Possible Disappearance

• (1) Fall line bedrock erodes between 6 and 9 meters per million years

• (2) Upland gravels above the fall line

• (3) Gradients show the fall line is stable

• Shifting plates and erosion/deposition in several million years (move FL)

• Next million years, the fall line should remain stable

The fall line’s significance

• Historically, the fall line was important in navigation and settlement

• First noticed when traveling by boat

• Colonized area to control trade and transportation (Columbia)

• Potential for hydrologic power and irrigation from fall line’s rivers

• Farms and SC’s economy

Pictures Cited• http://www.virginiaplaces.org/regions/fallshape.html

• Snipes et al., 1993

• https://pangaeablues.wordpress.com/author/pangaeablues/

• https://www.pinterest.com/xadams2/precambrian-hadean-4600-3800-miljoen-v-chr/

• http://bullet-magnet.deviantart.com/art/Planet-Icarus-Erebosian-Eon-48325388

• http://paristampablog.com/tag/paris-bassin/

• http://www.rci.rutgers.edu/~schlisch/103web/NJcontext/ENAhistory.html

• http://www.gns.cri.nz/Home/Learning/Science-Topics/Earthquakes/Earthquakes-and-Faults

• http://en.wikipedia.org/wiki/Fall_line

• http://www.postandcourier.com/article/20150411/PC1002/150419855/1022/stand-strong-for-sc-coast

• Odum et al., 2013

• http://www.georgiaencyclopedia.org/blog/2013/08/13/rolling-line